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x86/show_trace_log_lvl: Ensure stack pointer is aligned, again

Oleg Nesterov requested to merge onestero/centos-stream-9:show_trace_log_lvl into main

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2188506 Upstream-status: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

commit 2e4be0d011f21593c6b316806779ba1eba2cd7e0 Author: Vernon Lovejoy vlovejoy@redhat.com Date: Fri May 12 12:42:32 2023 +0200

x86/show_trace_log_lvl: Ensure stack pointer is aligned, again

The commit e335bb51cc15 ("x86/unwind: Ensure stack pointer is aligned")
tried to align the stack pointer in show_trace_log_lvl(), otherwise the
"stack < stack_info.end" check can't guarantee that the last read does
not go past the end of the stack.

However, we have the same problem with the initial value of the stack
pointer, it can also be unaligned. So without this patch this trivial
kernel module

        #include <linux/module.h>

        static int init(void)
        {
                asm volatile("sub    $0x4,%rsp");
                dump_stack();
                asm volatile("add    $0x4,%rsp");

                return -EAGAIN;
        }

        module_init(init);
        MODULE_LICENSE("GPL");

crashes the kernel.

Fixes: e335bb51cc15 ("x86/unwind: Ensure stack pointer is aligned")
Signed-off-by: Vernon Lovejoy <vlovejoy@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20230512104232.GA10227@redhat.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Signed-off-by: Oleg Nesterov oleg@redhat.com

Edited by Alex Gladkov

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